Tank filters placed in series with the lead wires or circuits of active medical devices to enhance MRI compatability

Abstract

A TANK filter is provided for a lead wire of an active medical device (AMD). The TANK filter includes a capacitor in parallel with an inductor. The parallel capacitor and inductor are placed in series with the lead wire of the AMD, wherein values of capacitance and inductance are selected such that the TANK filter is resonant at a selected frequency. The Q of the inductor may be relatively maximized and the Q of the capacitor may be relatively minimized to reduce the overall Q of the TANK filter to attenuate current flow through the lead wire along a range of selected frequencies. In a preferred form, the TANK filter is integrated into a TIP and/or RING electrode for an active implantable medical device.

What is claimed is: 
     
       1. A hermetically sealed feedthrough terminal for an active implantable medical device, the feedthrough terminal comprising:
 a) a ferrule; 
 b) a conductor passing through the ferrule in nonconductive relation, wherein the conductor comprises a hermetic seal separating a body fluid side from a device side; and 
 c) a TANK filter electrically coupled in series along the conductor, wherein the TANK filter is disposed at, near or within the ferrule. 
 
     
     
       2. The terminal of  claim 1  wherein the TANK filter is disposed along the device side protected from a patient's bodily fluids. 
     
     
       3. The terminal of  claim 1  including a feedthrough capacitor attached to the ferrule disposed on the device side. 
     
     
       4. The terminal of  claim 3  wherein the feedthrough capacitor comprises at least one active electrode plate and at least one ground electrode plate disposed within a dielectric substrate. 
     
     
       5. The terminal of  claim 4  wherein the at least one ground electrode plate is electrically coupled to the ferrule. 
     
     
       6. The terminal of  claim 5  wherein the at least one active electrode plate is electrically coupled to the conductor. 
     
     
       7. The terminal of  claim 6  wherein the TANK filter is disposed at, near or within the feedthrough capacitor. 
     
     
       8. The terminal of  claim 1  wherein the TANK filter comprises a self-resonant inductor comprising an inductance in parallel with a capacitance selected so as to be resonant at or near a frequency or over a range of frequencies of electromagnetic radiation. 
     
     
       9. The terminal of  claim 8  wherein the frequency or the range of frequencies comprise an MRI RF frequency or range of MRI RF frequencies. 
     
     
       10. The terminal of  claim 1  wherein the TANK filter comprises a self-resonant inductor, wherein a TANK filter inductance is formed by an insulated coiled or spiral inductor, and wherein a TANK filter capacitance comprises a parasitic capacitance between adjacent turns of the insulated coiled or spiral inductor. 
     
     
       11. The terminal of  claim 1  wherein the TANK filter comprises a discrete inductor component in parallel with a discrete capacitor component. 
     
     
       12. A hermetically sealed feedthrough terminal for an active implantable medical device, the feedthrough terminal comprising:
 a) a ferrule; 
 b) an insulator attached inside the ferrule; 
 c) a conductor passing through the insulator in nonconductive relation to the ferrule; 
 d) at least one hermetic seal between the insulator and the conductor separating a body fluid side from a device side; and 
 e) a TANK filter electrically coupled in series along the conductor, wherein the TANK filter is disposed at, near or within the ferrule. 
 
     
     
       13. The terminal of  claim 12  wherein the TANK filter is disposed along the device side protected from a patient's bodily fluids. 
     
     
       14. The terminal of  claim 13  including a feedthrough capacitor attached to the ferrule on the device side. 
     
     
       15. The terminal of  claim 14  wherein the feedthrough capacitor comprises at least one active electrode plate and at least one ground electrode plate disposed within a dielectric substrate. 
     
     
       16. The terminal of  claim 15  wherein the at least one ground electrode plate is electrically coupled to the ferrule. 
     
     
       17. The terminal of  claim 16  wherein the at least one active electrode plate is electrically coupled to the conductor. 
     
     
       18. The terminal of  claim 17  wherein the TANK filter is disposed at, near or within the feedthrough capacitor. 
     
     
       19. The terminal of  claim 12  wherein the TANK filter comprises a self-resonant inductor comprising an inductance in parallel with a capacitance selected so as to be resonant at or near a frequency or over a range of frequencies of electromagnetic radiation. 
     
     
       20. The terminal of  claim 19  wherein the frequency or the range of frequencies comprise an MRI RF frequency or range of MRI RF frequencies. 
     
     
       21. The terminal of  claim 12  wherein the TANK filter comprises a self-resonant inductor, wherein a TANK filter inductance is formed by an insulated coiled or spiral inductor, and wherein a TANK filter capacitance comprises a parasitic capacitance between adjacent turns of the insulated coiled or spiral inductor. 
     
     
       22. The terminal of  claim 12  wherein the TANK filter comprises a discrete inductor component in parallel with a discrete capacitor component. 
     
     
       23. A hermetically sealed feedthrough terminal for an active implantable medical device, the feedthrough terminal comprising:
 a) a ferrule; 
 b) an insulator attached inside the ferrule; 
 c) a conductor passing through the insulator in nonconductive relation to the ferrule; 
 d) at least one hermetic seal between the insulator and the conductor separating a body fluid side from a device side; 
 e) a feedthrough capacitor attached to the ferrule on the device side, the feedthrough capacitor comprising at least one ground electrode plate and at least one active electrode plate disposed within a dielectric substrate, wherein the at least one ground electrode plate is electrically coupled to the ferrule and the at least one active electrode plate is electrically coupled to the conductor; and 
 f) a TANK filter electrically coupled in series along the conductor on the device side protected from a patient's bodily fluids, wherein the TANK filter is disposed at, near or within the ferrule. 
 
     
     
       24. The terminal of  claim 23  wherein the TANK filter comprises a self-resonant inductor comprising an inductance in parallel with a capacitance selected so as to be resonant at or near an MRI RF frequency or over a range of MRI RF frequencies of electromagnetic radiation. 
     
     
       25. The terminal of  claim 23  wherein the TANK filter comprises a self-resonant inductor, wherein a TANK filter inductance is formed by an insulated coiled or spiral inductor, and wherein a TANK filter capacitance comprises a parasitic capacitance between adjacent turns of the insulated coiled or spiral inductor. 
     
     
       26. The terminal of  claim 23  wherein the TANK filter comprises a discrete inductor component in parallel with a discrete capacitor component. 
     
     
       27. An active implantable medical device (AIMD), the active implantable medical device comprising:
 a) a hermetically sealed housing comprising an electronic circuit disposed within the housing; 
 b) a ferrule hermetically sealed to the housing; 
 c) an insulator attached inside the ferrule; 
 d) a conductor passing through the insulator in nonconductive relation to the ferrule and electrically coupled to the electronic circuit; 
 e) at least one hermetic seal between the insulator and the conductor separating a body fluid side from a device side; and 
 f) a TANK filter electrically coupled in series along the conductor on the device side protected from a patient's bodily fluids, wherein the TANK filter is disposed at, near or within the ferrule, wherein the TANK filter comprises an inductance in parallel with a capacitance selected so as to be resonant at or near an MRI RF frequency or over a range of MRI RF frequencies of electromagnetic radiation. 
 
     
     
       28. The AIMD of  claim 27  including a lead removably or permanently electrically coupled to the electronic circuit, the lead comprising a proximal end attached near the housing and extending to a distal end comprising an electrode adapted for contact with biological cells. 
     
     
       29. The AIMD of  claim 28  wherein the lead comprises a second TANK filter attached near the distal end, wherein the second TANK filter comprises an second inductance in parallel with a second capacitance selected so as to be resonant at a second MRI RF frequency or over a second range of MRI RF frequencies of the electromagnetic radiation. 
     
     
       30. A hermetically sealed feedthrough terminal for an active implantable medical device, the feedthrough terminal comprising:
 a) a hermetically sealed conductive housing containing at least one electronic circuit disposed within the housing; 
 b) an insulator attached inside an opening in the housing; 
 c) a conductor passing through the insulator in nonconductive relation to the housing; 
 d) at least one hermetic seal between the insulator and the conductor separating a body fluid side from a device side; 
 e) a feedthrough capacitor attached to or near the insulator on the device side, the feedthrough capacitor comprising at least one ground electrode plate and at least one active electrode plate disposed within a dielectric substrate, wherein the at least one ground electrode plate is electrically coupled to the housing and the at least one active electrode plate is electrically coupled to the conductor; and 
 f) a TANK filter electrically coupled in series along the conductor on the device side protected from a patient's bodily fluids, wherein the TANK filter is disposed at, near or within the housing. 
 
     
     
       31. The terminal of  claim 30  wherein the TANK filter comprises a self-resonant inductor comprising an inductance in parallel with a capacitance selected so as to be resonant at or near an MRI RF frequency or over a range of MRI RF frequencies of electromagnetic radiation. 
     
     
       32. The terminal of  claim 30  wherein the TANK filter comprises a self-resonant inductor, wherein a TANK filter inductance is formed by an insulated coiled or spiral inductor, and wherein a TANK filter capacitance comprises a parasitic capacitance between adjacent turns of the insulated coiled or spiral inductor. 
     
     
       33. The terminal of  claim 30  wherein the TANK filter comprises a discrete inductor component in parallel with a discrete capacitor component. 
     
     
       34. An active implantable medical device, comprising:
 a) a hermetically sealed housing defined as comprising a perimeter surface separating a body fluid side from a device side; 
 b) a conductor passing through the housing in nonconductive relation; and 
 c) a TANK filter electrically coupled in series along the conductor disposed at, near or within the perimeter surface of the housing. 
 
     
     
       35. The active implantable medical device of  claim 34  wherein the TANK filter is disposed along the device side protected from a patient's bodily fluids. 
     
     
       36. The active implantable medical device of  claim 35  wherein the TANK filter comprises a self-resonant inductor comprising an inductance in parallel with a capacitance selected so as to be resonant at or near an MRI RF frequency or over a range of MRI RF frequencies of electromagnetic radiation. 
     
     
       37. The active implantable medical device of  claim 35  wherein the TANK filter comprises a self-resonant inductor, wherein a TANK filter inductance is formed by an insulated coiled or spiral inductor, and wherein a TANK filter capacitance comprises a parasitic capacitance between adjacent turns of the insulated coiled or spiral inductor. 
     
     
       38. The active implantable medical device of  claim 35  wherein the TANK filter comprises a discrete inductor component in parallel with a discrete capacitor component.